1. Field of the Invention
The present invention relates to an image forming apparatus which allows margin-less printing for printing on a printing material without margin and, more particularly, to an image forming apparatus which allows double-sided printing without margin.
2. Description of the Related Art
Recent inkjet and bubble-jet® printers can form an image on the entire surface of a printing material. This scheme is called margin-less printing because no margin is formed at the peripheral portion of a printing material. There is also proposed an approach to such margin-less printing, in which an electrophotographic image forming apparatus forms a developer image to be larger than a printing material and transfers it onto the printing material.
Japanese Patent Laid-Open No. 2004-45457 discloses an electrophotographic image forming apparatus which attains margin-less printing by forming a developer image to be larger than a printing material. The technique described in Japanese Patent Laid-Open No. 2004-45457 forms a developer image sufficiently larger than a printing material, so the printing material has no margin even when the developer image is slightly misaligned with respect to the printing material.
However, since the image forming apparatus described in Japanese Patent Laid-Open No. 2004-45457 forms a developer image sufficiently larger than a printing material, it wastes a portion of the developer (toner) which is not transferred onto the printing material. Especially, for example, when the size of a printing material to be conveyed is unknown before the start of printing, a conventional image forming apparatus forms a developer image to match the maximum size of a printable printing material in printing. Therefore, when the conventional image forming apparatus prints a printing material whose size is unknown but is actually small, it produces a large amount of toner which is not transferred onto the printing material. That is, when the conventional image forming apparatus performs margin-less printing for a printing material whose size is unknown, it consumes toner in very large quantities.
An electrophotographic image forming apparatus, in particular, generates a double-sided printed printing material having dimensions in the main scanning direction and sub scanning direction which have slightly shortened upon fixing processing in printing on the first page. The dimensions of the printing material decrease because the printing material shrinks due to heat in the fixing processing. This makes an image forming region of the printing material in printing on the second page narrower than that on the first page. However, the conventional image forming apparatus forms developer images on the first and second pages with the same size in margin-less printing. A larger amount of waste toner is cleaned and recovered without being transferred onto the printing material in margin-less printing on the second page than in printing on the first page. A portion of the developer (the developer image which is not transferred onto the printing material) formed outside the printing material mainly accounts for the toner wasted in margin-less printing.